Speaker enclosure



Feb. 8, 1966 R. E. HUTCHINS SPEAKER ENCLOSURE Filed July 10, 1964 FIG. 2

FIG.

FIG. 4

FIG. 3

INVENTOR. RALPH E. HUTCHINS HIS ATTORNEYS.

United States Patent The invention relates to an improved speakerenclosure and particularly to a speaker enclosure having a vibratilepanel for improving the musical sounds, and

especially the bass sounds, produced by such enclosure in cooperationwith a speaker.

The physics and behavior of speaker enclosures are 'not completelyunderstood and have been the subject of much controversy in the past. Nosingle authoritative reference answers all the theoretic-a1 questions inthe speaker enclosure field, and many variables such as different typesof woods and other construction materials, glues, fasteners, shapes,braces, etc., remain relatively unexplored. There have been many priorart attempts at the design of a satisfactory speaker enclosure, but mostof them have been relative failures, or rather poor compromises. Theyhave sulfered from poor bass response, uneven response including harshresonances or booms, and various unpleasant sounds and distortions. Inaddition to relatively poor performance, all of the speaker cabinets andbaflles proposed thus far have drawbacks such as impractical size,weight, or cost. Also, they have failed to accomplish an optimumsolution to the classic problem of cancellation of the back wave of thespeaker at low frequencies. Attempts at directing back radiation fromthe speaker cone around a suitable baffle so as to bring it intoreinforcing relation with front radiation from the speaker have beenonly partially successful and have produced uneven response,

One of the best comprises to date is the ported cabinet or bass reflexspeaker enclosure comprising a rather large, closed cabinet asacoustically rigid as practical and having an open port for radiatingthe back wave of the speaker. Some of the drawbacks of a bass reflexspeaker enclosure include disagreeable resonant peaks in its output andimpractical size and weight.

It is an object of this invention to overcome the deficiencies of theprior art speaker enclosures in providing a relatively small, lightweight, speaker enclosure of simple and inexpensive construction ableeffectively to use the back radiation of the speaker in reinforcingrelation with the front radiation for producing a flat, full bassresponse without distortion or disagreeable booms, wolf notes, orresonances.

Another object of the invention is to add to and alter in a musicallypleasant way the harmonic structure of musical sounds produced by aspeaker.

Another object of the invention is to mechanically invert the phase of apreselected range of low frequency sound radiation from the back of aspeaker and radiate such low frequency radiation from the speakerenclosure in phase with the front radiation of the speaker forreinforcing the lower frequency ranges of music produced by the speaker.

Another object of the invention is to use back radiation from a speakercone for driving a vibratile panel substantially in phase with thespeaker cone throughout a preselected low range of frequencies.

Another object of the invention is to control the resonance of a speakerenclosure so that it has a relatively uniform response to all musicalfrequencies and produces sound that is musically pleasing.

Another object of the invention is to provide a speaker enclosure with apanel that is vibratable in phase with the cone of the speakerthroughout a predetermined low range of frequencies so as to attenuatespeaker cone excursion and thereby allow more power to be applied to thespeaker without overdrive or intermodulation distortions.

Another object of the invention is to use a speaker enclosure to adddepth and quality to the low frequency musical sound produced by thespeaker and to correlate the speaker and the enclosure so as to producepleasing musical sounds at all musical frequencies.

Another object of the invention is to extend the high frequency responseof a speaker that has a relatively low resonant frequency.

Other objects of the invention will be apparent hereinafter from thespecification and from the recitals of the appended claims. To these andother ends, the invention resides in certain improvements andarrangements of parts, all as will be hereinafter more fully described,the novel features being pointed out in the claims at the end of thespecification.

In the drawings:

FIG. 1 shows an isometric rear view of a speaker enclosure according tothe invention;

FIG. 2 shows the view of FIG. 1 with the back and side panels removedfrom the speaker enclosure;

FIG. 3 shows a partially sectioned side elevation of a panel of thespeaker enclosure according to the invention;

FIG, 4 shows a cross section of the panel of FIG. 3 taken along the line4-4;

FIG. 5 shows a cross section of the panel of FIG. 3 taken along the line5-5; and

FIG. 6 shows an exaggerated flexure of the panel as viewed in FIG. 5.

Generally, the invention is accomplished by making a boundary of aspeaker enclosure function as a vibratile panel having a plurality ofmodes of vibration including the mode of a reed and using the backradiation from the speaker to vibrate the panel substantially in inversephase relation with the back radiation throughout predetermined lowrange of frequencies.

In the following description of the invention the con struction detailsof an illustrative speaker enclosure according to the invention willfirst be described, and then operation of the enclosure will bediscussed.

Construction of enclosure As shown in FIGS. 1 and 2, a speaker enclosure10 is formed of a plurality of panels 11, 12, 13, 14, 16, and 17 thatare preferably rectangular, but can be any convenient shape. The panels1144, 16, and 17 are preferably formed of wood but may be of any othersuitable material, and are fastened together and to frame members 1843in any acceptable manner such as by glue and screws. As oriented inFIGS. 1 and 2, the enclosure includes a top 11, bottom 12, side 13,front 14, back 16, and side panel 17. The enclosure as illustrated inFIG. 2, is shown with back panel 16 and side panel 17 removed, revealingthe back of a speaker 15. Speaker 15 is mounted over an aperture (notshown) in front panel 14 for radiating sound from the front of speaker15 into the general area in front of panel 14. Back radiation of soundfrom speaker 15 is exhausted into the interior of enclosure 10.

Panel 17 could form the outside panel of the speaker enclosure 10, butsince structural members are outboard of panel 17, panel 24, spaced frompanel 17, is added to improve the appearance of the enclosure 10 as apiece of furniture. The space between panel 17 and panel 24 can be usedfor mounting an amplifier or another speaker.

As shown in FIGS. 1 and 3, the back edge of vibratile panel 17 issupported or fixed in place by being connected to back panel 16 by meansof screws 25. Between back panel 16 and vibratile panel 17 is preferablyarranged a strip of foam rubber 27 through which screws .25 pass. Screws25 are preferably round head screws that can be tightened or loosenedfor adjusting the tension or the rigidity of the connection between backpanel 16 and vibratile panel 17. Screws 26 fasten back panel 16 to framemembers 18, 19, and 23, from which back panel 16 is preferably spaced bya strip of foam rubber.

As best shown in FIGS. 36, the front edge of vibratile panel 17 is freeto move or vibrate and is not connected to other frame members orpanels. A foam rubber strip 28 is preferably placed around the top,bottom, and front edges of panel 17 so as to extend the periphery ofpanel 17 to closely fit top 11, bottom 12, and front 14 so as toeffectively and substantially close in a volume of air within thespeaker enclosure 10. The portions of panels 11, 12, and 14 over whichpanel 17 moves when vibrating are preferably finished smooth for exampleby sanding and coating with a smooth lacquer. Also, a dry lubricant suchas talcum powder is preferably applied to foam rubber strip 23 or to theportions of panels 11, 12, and 14 over which foam rubber strip 28 moves,to insure easy movement and vibration of panel 17 while maintaining aclose fit between panel 17 and adjacent panels.

As illustrated in FIGS. 3-6 vibration of panel 17 is controlled andsomewhat modified by resilient gripping means or dampers 29 engagingpanel 17 along its top and bottom edges for a portion of the distancefrom the back edge to the front edge of panel 17. Each damper 29 ispreferably formed of wood and has a strip of foam rubber Ell bondedthereto. Dampers 29 are fastened to top panel 11 and bottom panel 12 insuch a way that foam rubber strips 3% face inward and engage panel 17for controlling its vibrating motion.

The dampers 29 require that panel 17 not vibrate in one piece in themotion of a swinging door but rather in a more complex manner includinga plurality of modes. To facilitate such vibration it is preferred thatpanel 17 be formed of flexible material, and in one successfulembodiment of the invention, panel 17 was formed of /8" plywood with thegrain of the outer layers of the plies running from front to back of thepanel 17. With proper adjustment of dimensions and other parameters,other materials, woods, or grain orientations may be used for panel 17.7

Operation All the details as to the operation of the inventive speakerenclosure, and the complete theoretical explanation of its functioningare not known. The invention was arrived at empirically after manyinoperable variations and unsuccessful attempts. As mentioned above,acoustic theory with respect to speaker enclosures generally isincomplete and somewhat confused. The following de scription of theoperation of the inventive enclosure is as complete and accurate aspresently known, and is offered to make the operation of the inventionas clearly understandable as possible. However, applicant does not wishto be limited to any particular theory or rationale as to the operationof the inventive speaker enclosure or the reasons for its improved soundproducing ability. There is a great deal of empirical evidence andexpert opinion in support of the fact that the inventive speakerenclosure does cooperate with a speaker to produce musical sounds thatare more pleasing to listeners, and many presently known and possiblefuture explanations help account for this.

Panel 17 is driven or vibrated by the back wave or back radiation fromspeaker 15. The mass, flexibility, rigidity of mounting, and otherfactors contributing to the reluctance of panel 17 to move are arrangedso that for frequencies from about 30 cycles per second or the bottom ofthe range of musical sounds up to about 200 to 250 cycles per second,panel 17 is vibrated substantially in phase with the cone of speaker 15.This occurs in part because when the cone of speaker 15 moves into theenclosure so as to cause a compression within the enclosure, suchcompression is transmitted by the enclosed volume of air to the walls ofthe enclosure and within a finite time produces an outward push on panel17. Because of the delay in the transmission of the compression, andbecause of the size and reluctance of panel 17 to move, by the timepanel 17 starts its actual outward motion in response to the push fromthe compression, the speaker cone is also moving or about to moveoutward. The outward movement of the speaker cone causes a rarefactionwithin the enclosure which effectively exerts an inward pull on panel17. By the time panel 17 actually moves inward in response to such pull,the speaker cone is also moving inward.

The in-phase relationship of panel 17 with the cone of speaker 15 ismaintained throughout a range of three or four octaves at the bottom ofthe musical scale so that panel 17 has a fiat response to suchfrequencies without any sharp peaks or pronounced amplitude in itsresonance.

The panel 17 is not always exactly in phase with the front radiation ofspeaker 15 but has various small phase angles relative to the speakercone throughout the three to four octaves at the bottom of the musicalscale. By such an in-phase relationship the panel 17 reinforces and addsto sound radiated from the front of speaker 15.

A mechanical analogy to the in-phase relationship between panel 17 andthe cone of speaker 15 can be made by depending a weight from a spring.By correct selection of weight and spring, it is possible to oscillatethe weight in-phase with the oscillation of the top of the spring sothat the top of the spring and the weight move toward and away from eachother similarly to the way the cone of speaker 15 and vibratile panel 17move toward and away from each other.

It would be possible to vary the size, mass, flexibility, etc., ofvibratile panel 17 so as to tune it for in-phase vibration with speaker15 at frequencies other than low frequency ranges, but it is the musicallows rather than the highs and medium highs which most need boosting orreinforcing by the speaker enclosure. This is caused in part by the factthat the resistive component of air relative to cone diameter is reducedfor frequencies below which the cone diameter is about one-half wavelength.

FIGS. 4-6 partially illustrate the vibration of panel 17. The basic lowfrequency phase inversion, or in-phase vibration of panel '17 asdescribed above can be characterized as a predominantly reed-typevibration. Thus, panel 17 can be considered as a relatively long, widereed fastened at its back edge by screws 25 and free to vibrate at itsfront edge. FIG. 6 shows a view of an exaggerated flexure of panel 17 inresponse to such vibration. This basic, reed-type vibration is somewhatmodified by dampers 29 which tend to form funnel or valleyconfigurations in the panel as the front portion vibrates. This can beseen from the view of FIG. 4 showing that the forward portion of panel17 can vibrate with the greatest amplitude at the center of the paneland with reduced amplitude toward its top and bottom edges. The valleyor funnel configurations produce corresponding, but smaller, hillportions raised in the rearward sectors of the panel. This can be seenin FIG. 6 where, in the illustrated position of panel 17, the foamrubber strips 30 of dampers 29 are shown compressed at the lower forwardedge and the upper central portion of the dampers 29, the upper centralcompression being the hill portions mentioned above. In other words, asthe front portion of panel 17 moves in one direction, some portions ofits rearward area move in the opposite direction. Partly because of theanchoring of the rear edge of the panel by screws 25; panel 17 is bentor flexed in the performance of such vibration rather than moving as onesolid piece around a fulcrum point established by the dampers 29.

The vibratile panel 17 is known to have other vibra- I tion modes atsome frequencies. For example, substantial portions of it can vibratesubstantially in one piece with little fiexure in the mode of a pistonor plate with smaller amplitude vibrations that are most easily detectedat-higher frequencies. Also, the front portion of panel 17 can have acentral node around which its upper and lower portions travel inopposite directions. Furthermore, above the range of frequencies forwhich the basic reed-type vibration of panel 17 is in phase with' thecone of speaker 15, central and rearward areas of panel 17 were found tobe in phase with the speaker cone. All the vibrations of the panel havenot been analyzed, and much time, equipment, and study would be requiredto analyze definitively all the vibrations in response to allfrequencies and all combinations of musical tones. It has been clearlydetermined, however, that the vibrations of the panel are basically inphase with the speaker cone throughout the lower three to four octavesof the musical scale, and that it cooperates with the speaker and therest of the enclosure to alter or add to the harmonic structure of themusical input to the speaker. This is particularly true for the musicproduced by electronic instruments such as organs, accordions, andguitars.

For many musical tones, particularly in the low musical ranges, thevibrations of panel 17 increase the amplitude of harmonics in such a wayas to produce a resultant lower tone apparently an octave below thefundamental and thus deepen and add quality to bass notes in a musicallypleasant way. Bass tones produced by the panel 17 in cooperation withthe speaker enclosure have authority, volume, and quality adjudgedremarkable and exceptionally pleasing and desirable by musicians andmusical experts.

An important effect of the above described in-phase vibration of panel17 relative to the cone of speaker is that speaker cone excursion isattenuated. As the cone of speaker 15 is moving inward to produce acompressioninside the enclosure 10, panel 17 also is moving inward andalso produces a compression within the enclosure 10. This effectivelycushions the cone of speaker 15. An opposite, similar effect is obtainedfor the outward travel of the speaker cone. Several important advantagesresult from such cone excursion attenuation. Speaker 15 can be drivenwith more than normal power without its cone excursion exceeding thelimits within which the speaker response is linear. Distortionintroduced by the cones spider is also reduced, and harsh, unpleasantintermodulation distortion is substantially eliminated.

In effect, the speaker cone is coupled to the panel 17, so that some ofthe power applied to the speaker is used to drive panel 17 in anin-phase relationship rather than merely to force the speaker conethrough a long excursion. The relatively large area of panel 17(approximately three or four times the area of the speaker cone) is usedas the primary radiator of low frequencies, thus substantially solvingthe well known problem of long speaker cone excursion for lowfrequencies. As illustrating the capacity of the inventive speakerenclosure to eliminate various distortions by reducing speaker coneexcursion, a 21 watt speaker mounted in speaker en closure 10 has beendriven at peaks of 90 watts and with an average input of 50 wattswithout any substantial distortion or unpleasantness in the musicaloutput. This capacity of the inventive speaker enclosure can reduce theexpense and complexity of speakers and enclosures for high poweredoutput.

Back panel 16 cooperates with the speaker 15 and with side panel 17 andthe rest of the speaker enclosure to act as a musical sounding board. Aspeaker enclosure such as enclosure 10 previously would have to havebeen built as acoustically rigid as practical to avoid unpleasantdistortions and objectionable resonant peaks at a few particularfrequencies. In contrast, back panel 16 can be formed of fairly lightmaterial, for example /2 plywood, and can be resiliently mounted as byinterposing a foam rubber strip around the periphery of back panel 16between it and panel 17 and the frame members 18, 19, and 23 to which itis fastened. Side panel 17, by consuming much of the power input to thespeaker 15 at low frequencies and by vibrating in an in-phase relationwith the cone of speaker 15 so as to reduce the excursion of such cone,thereby not only reduces intermodulation distortion in the speaker cone,but also similar intermodulation distortion in the vibration of backpanel 16. In effect, the large amplitude, long vibrations for the basstones are provided by side panel 17, and back panel 16, relieved of suchforces, can respond as a resonant sounding board having generallyplate-type vibrations that are more responsive to higher frequencies andare relatively uniform with musically pleasant characteristics.

An observed characteristic of the speaker enclosure according to theinvention, the reasons for which are presently unknown, is that thespeaker enclosure 10 also extends the high frequency response of awoofer type speaker having a relatively low resonant frequency, forexample 30 to 40 cycles per second.

Conventional speaker enclosures and baflle structures exhibit tworesponse peaks in their musical output, one peak corresponding to thenatural resonant frequency of the enclosure or baffle structure, and theother corresponding to the natural resonant frequency of the speakercone. The usual procedure is to design the baffie or enclosure so thatit has a natural resonant frequency below that of the speaker cone inorder to separate the two response peaks, providing a smoother frequencyresponse and minimizing the boom effect characteristic of a sharp peakin the frequency response in the bass region. Speaker enclosure 10 addsthree resonant bodies not present in the conventional enclosure orbafile structures: 1) the natural resonance of the back panel soundingboard 16, (2) the natural resonance of the volume of air confined in theenclosure, and (3) the resonance of vibratile panel 17 with its complexvibrations in the modes of both a reed and a plate. By properly spacingthe naturally resonant frequencies of all five bodies, a relatively flatresponse can be produced over a wider range of frequencies than can beobtained from an enclosure or baflie structure of conventional design.

Final tuning of any speaker enclosure or bafiie, like tuning of amusical instrument, has always required some empirical modification andadjustment to produce optimum musical quality. Variation in size, shape,materials, construction techniques, etc, in the manufacture of speakerenclosures according to the invention will probably also require sometuning for best results. In addition to tuning by changing dimensionssuch as panel and enclosure sizes and the length of dampers 29, tuningcan also be effected by the tension of screws 25 connecting back panel16 and side panel 17, compression of foam rubber strips 30 of dampers 29against the top and bottom edges of panel 17 and changes in materials,wood grain orientations, and speaker characteristics.

Obviously, vibratile panel 17 and other enclosure panels such as backpanel 16 can be changed in orientation or position. Thus, vibratilepanel 17 can be located at the back, top, bottom, or front of enclosure10, or could be secured at its front edge and have its back edge free tomove. The back panel sounding board 16 can be arranged and secured inmany other ways, and can even be made relatively rigid with excellentsound production resulting. Variations in the ways of securing vibratilepanel 17 and controlling or damping its vibrations are also possiblewithin the spirit of the invention.

Accordingly, while the invention has been disclosed herein by referenceto the details of a preferred embodiment thereof, it is to be understoodthat such disclosure is intended in an illustrative rather than alimiting sense, and it is contemplated that various modifications in theconstruction and arrangement of the parts will readily ocour to thoseskilled in the art within the spirit of the invention and the scope ofthe appended claims.

I claim:

1. A substantially closed speaker enclosure a boundary of whichcomprises a substantially rectangular panel resiliently supported alongone edge thereof and along adjacent portions of each edge of said panelthat adjoins said one edge, so that said panel is vibratile in the modeof a relatively wide reed and in the mode of a plate.

2. A speaker enclosure substantially confining a volume of air andincluding a speaker having a vibratile cone the back of which is incommunication with said volume of air, a boundary of said enclosurecomprising a substantially rectangular panel resiliently supported alongone edge thereof and along adjacent portions of each edge of said panelthat adjoins said one edge, said panel being actuatable by sound wavesfrom said back of said cone for vibration in the mode of a reedsubstantially in phase with said cone throughout a predetermined lowrange of frequencies.

3. A substantially closed speaker enclosure formed of a plurality ofsubstantially rectangular panels a first one of which is resilientlysupported around its periphery for acting as a sounding board, and asecond one of which is resiliently supported along one edge thereof andalong adjacent portions of each edge thereof that adjoins said one edge,so that said second panel is vibratile in the mode of a relatively widereed.

4. A substantially closed speaker enclosure a boundary of whichcomprises a substantially rectangular panel supported along a first edgethereof and being free for vibrational movement along a second, oppositeedge thereof, said vibrational movement being damped by resilientmembers engaging said panel along each of the edges of said panelleading from said first edge to said second edge for a portion of thedistance from said first edge to said second edge.

5. A speaker enclosure having the structure specified in claim 4 whereinsaid panel is resiliently connected along said first edge thereof to asounding board forming another boundary of said enclosure, said soundingboard being resiliently supported around its periphery.

6. A speaker enclosure substantially confining a volume of air andincluding a speaker having a vibratile cone the back of which is incommunication with said volume of air, a boundary of said enclosurecomprising a substantially rectangular panel supported along a firstedge thereof and free for vibrational movement along a second, oppositeedge thereof, said vibrational movement being damped by resilientmembers engaging said panel along each of the edges of said panelleading from said first edge to said second edge for a portion of thedistance from said first edge to said second edge, the sound waves fromsaid back of said cone acting through said volume of air for causingsaid vibration of said panel substantially in phase with said conethroughout a predetermined low range of sound frequencies.

7. A substantially closed speaker enclosure formed of a plurality ofsubstantially rectangular panels, a first one of said panels beingresiliently supported around its periphery for acting as a soundingboard, and a second one of said panels being resiliently supported alonga first edge thereof and freely movable for vibration along a secondopposite edge thereof, vibratile movement of said second panel beingwarped by resilient members engaging said second panel along each of theedges of said panel leading from said first edge to said second edge fora portion of the distance from said first edge to said second edge. I

8. A speaker enclosure substantially confining a volume of air andsupporting a speaker having a vibratile cone the front of which is incommunication with ambient air outside said enclosure and the back ofwhich is in communication with said volume of air, vibration of saidcone being transmitted by said volume of air to the boundaries of saidenclosure, a first one of said boundaries comprising a sounding boardresiliently secured around its periphery to said enclosure through astrip of resilient material, and a second one of said boundariescomprising a panel a first edge of which is secured to said soundingboard through a strip of resilient material, a second opposite edge ofsaid second panel being free for vibration, said vibration of saidsecond panel being warped by resilient cleats engaging the edges of saidpanel leading from said first edge to said second edge for a portion ofthe distance from said first edge to said second edge, whereby vibrationof said second panel in response to vibration of said cone producessound waves in reinforcing relation with sound waves from said front ofsaid cone throughout a predetermined low range of frequencies.

9. A substantially closed speaker enclosure a boundary of whichcomprises a resilient panel held substantially in place continuouslyalong approximately one half its periphery and freely movable along theremainder of its periphery.

10. The speaker enclosure of claim 9 wherein said panel is substantiallyrectangular and is held along one edge thereof and along adjacentportions of each edge of said panel that adjoins said one edge.

11. A substantially closed speaker enclosure formed of a plurality ofpanels, a first one of whichis held substantially in place aroundsubstantially its entire periphery and a second one of which is heldsubstantially in place continuously along approximately one half itsperiphery and freely movable along the remainder of its periphery.

12. The speaker enclosure of claim 11 wherein said first and secondpanels are mutually adjacent and sub,- stantially rectangular, and saidsecond panel is held in place along one edge thereof and along adjacentportions of each edge thereof that adjoins said one edge.

References Cited by the Examiner UNITED STATES PATENTS 1,923,870 8/1933Kressmann l8131.l 2,476,572 7/ 1949 Wenzel 181-3 1.1 2,713,396 7/1955Tavares 181-31.1 2,757,751 8/1956 Tavares 18l--31.1 2,811,215 10/1957Rudd et al. 181-31.1 2,834,423 5/ 1958 Bradford 181-311 3,090,461 5/1963Gray 18131.1 3,150,739 9/1964 Dones 18131.1

LEO SMILOW, Primary Examiner.

1. A SUBSTANTIALLY CLOSED SPEAKER ENCLOSURE A BOUNDARY OF WHICHCOMPRISES A SUBSTANTIALLY RECTANGULAR PANEL RESILIENTLY SUPPORTED ALONGONE EDGE THEREOF AND ALONG ADJACENT PORTIONS OF EACH EDGE OF SAID PANELTHE ADJOINS SAID ONE EDGE, SO THAT SAID PANEL IS VIBRATILE IN THE MODEOF A RELATIVELY WIDE REED AND IN THE MODE OF A PLATE.